The present invention relates to a method of forming a metal or alloy coating around an elongated body by continuous hot dipping.
A variety of conventional methods are known for hot dipping of wire or sheet metal. For example, wire can be coated with zinc by an apparatus of the type illustrated in FIG. 1. In this apparatus, a wire indicated at 1 is pulled up vertically from a melt 2 through an accumulation of carbon powder or flux 3 on the surface of the bath 2. During hot dipping, oxidation at the surface of the melt is not negligible. The use of the carbon powder or flux 3 prevents not only oxidation, but also prevents oxidized film from being drawn up together with the wire 1 by squeezing the film under the weight of the carbon powder or flux at the point where the wire exits the bath. However, this technique is not applicable to high-speed operations because the wire 1 in such a case vibrates significantly, producing a gap between the wire and the inner surface of the carbon or flux deposit. As a result, oxidized film unavoidably forms, which adversely affects the appearance of the final product. Thick and uniform coating cannot be attained.
A thick coating can be produced by electroplating, but this method is not economical because it requires a high initial cost and is time consuming.
In the conventional method of forming a tin or solder coating on a wire by hot dipping, the wire is usually passed through a die to remove any oxidized film. However, this method can only produce a thin coating. Accordingly, a technique that ensures the formation of thick and uniform coating has been desired.